javascript

Ravi Patel

Hi All,

var a="40" +10;

var b= "40"- 10;

alert(a); =>4010

alert(b); =>30

why? can any one explain

3 Replies

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Upendra Pratap Shahi10y ago
Since the + operator will be handled left-to-right the decisions,When u put a string in left side then it will CONCATENATE the value on right side.

"-" operator complies from left to right direction. Here "-" operator is there, it tries to convert it to integer and perform subtraction. Both operates different way in javascript.
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Manas Mohapatra10y ago
var a="40" +10; // 4010
var a="40" +10 +2; // 40102

"+" operator complies from left to right direction. So when you put first value as string then it considers the whole variable will be string and it appends the values to it(means it concatenates the string).

var b= "40" - 10; // 30
var b= "40A" - 10; // NaN
var b= 10 - "40"; // -30

"-" operator complies from left to right direction. Here "-" operator is there, it tries to convert it to integer and perform subtraction. If you see second case it will throw NaN because it tries to convert to integer but it is not valid number. Both operates different way in javascript.
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Rajeesh Menoth10y ago
Hi Ravi,

Since the + operator will be handled left-to-right the decisions,When u put a string in left side then it will CONCATENATE the value on right side.

Example :

https://jsfiddle.net/3yzzyh6a/

Reference :

http://stackoverflow.com/questions/5961000/javascript-sign-concatenates-instead-of-giving-sum-of-variables
+1